Electrolytic capacitors, such as tantalum capacitors, are traditionally known for their high capacitance value and compactness. Typical components of a conventional electrolytic capacitor include a main capacitor body, an anode wire or body, an electrolyte, a cathode and a leadframe all molded together in an encapsulating resin package. The anode wire and leadframe of such capacitors form respective positive and negative electrical connections to the capacitor structure. In certain instances, the conduction path associated with the anode lead incorporates fusible protective aspects in the overall capacitor structure.
A known interest in providing tantalum and other types of electrolytic capacitors with internal protective fuses has been previously addressed. U.S. Pat. No. 5,011,067 (Foisy) entitled “Method For Attaching A Fuse Wire To A Leadframe” discloses a tinned nickel-iron alloy lead frame having a plurality of pairs of extending tab portion positioned in a straight row. A long straight piece of an exothermically alloyable fuse wire, with a core of aluminum coaxially clad with palladium in approximately equal volumes, is held in contact with the plurality of pairs of lead frame tabs. Heat is applied to the fuse strand at two points; namely, on one and the other sides of each pair of tabs initiating progressive alloying in two directions from each heated point. When the progressive alloying and melting of the fuse strand reaches a tab, the tab is heated and heat sinks the fuse strand to stop the progressive alloying and melting. There is simultaneously formed a metallurgical bond between the ends of each remaining elemental fuse strand, respectively, and each of the pair of tabs that are bridged by that remaining elemental strand.
U.S. Pat. No. 4,899,258 (Gouvernelle) entitled “Solid Electrolyte Capacitor With Integral Fuse” discloses a solid electrolyte capacitor body embedded in an electrically insulative block of resin. Output terminals each connected to a respective electrode of the capacitor body project from the block. One output terminal includes a first section fixed to one of the electrodes and a second section electrically insulated from the first section and the capacitor body. A fusible member alone establishes electrical connection between the first and second sections. The fusible member is embedded in a rigid thermally insulative resin which extends between the first and second sections to couple them together mechanically.
U.S. Pat. No. 5,166,656 (Badihi et al.) entitled “Thin film Surface Mount Fuses” discloses fuses having consistent operating characteristics that are fabricated by forming a repeating lithographic fuse element pattern on an insulative substrate, passivating the structure, bonding a protective glass plate over the passivation layer, slicing the assembly so formed, terminating the slices and cutting the slices into individual fuses. Fuses thus manufactured may be of any desired dimensions, including standard and non-standard chip sizes.
U.S. Pat. No. 5,095,297 (Perreault et al.) entitled “Thin Film Fuse Construction” discloses a fuse including a fuse casing, an end cap terminal at an end of the casing, a substrate supporting a thin film fusible element thereon, and a disk component that is located at the end of the casing inside of the end cap terminal and has structure that defines a slot and engages an end of the substrate between opposing portions of the structure.
The prevalent desire to provide fusible protective features has, however, raised other issues including unintended increases in the overall equivalent series resistance (ESR) of the finished devices. In addition, the prior art devices have provided capability for only fixed or single fuse values for the finished devices.
While examples of various aspects and alternative embodiments are known in the field of fused electrolytic capacitors, no one design has emerged that generally encompasses all of the above-referenced and other preferred capacitor characteristics.